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BG Horn Mk1 - 36hz Front loaded horn

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citizensc View Drop Down
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    Posted: 22 June 2020 at 3:46am
Hi Guys

I have made this thread as a place to access the plans and ask questions about the BG Horn. 

PM me if either of the below links go dead.




What is the BG Horn? 
It is a 15 inch front loaded horn covering ~36-90hz. It is designed for the 15BG100. It has similar folding to a Punisher but is larger, more sensitive, plays lower, and should take more power. 

Why should you build the BG Horn?
-You need a FLH that plays below 40hz
-You want to build a FLH but other designs look too complex and hard to build
-You want a FLH that that is a manageable size and weight, the BG Horn is about 75kg loaded
-You would rather not spend big money on they types of drivers that are popular in DIY horns (pd.1850, V18-1000, 18sw115 etc.)
-You want to build a horn with a driver that is widely available and is likely to stay that way for some time
-You don't live in Europe or the US and find it difficult to get good quality 18 inch drivers due to air freight restrictions. 

Why shouldn't you build a BG Horn?
-You don't feel comfortable with building untested design. If you would like to give this plan a try, hit me up via PM or comment in this thread, id love to hear about it! 
-You plan to build less than 4 cabs, this may work okay with two cabs but is designed to work in groups of 4 or more. 
-You need a cab that is a one man lift (build single reflex cabs if you want this) 
-You are looking for a one-way bass solution that plays above 100hz. 


Here are some sims show where it fits - keep in mind that speaker design is about compromise, these cabs are all different size, efficiency, bandwidth and cost compromises. 

All sims are 2.83v @ 8 ohm (1 watt), 4 cabs grouped, 0.25 watt per cab. 

Punisher (12.00sw) Black, BG horn grey

1850 horn (pd.1850) Black, BG Horn Grey

WSX (V18-1000) black, BG Horn Grey

SBH (PD.1850) Black, BG Horn Grey

TH18 (18sw115-8) Black, BG Horn Grey




Edited by citizensc - 07 January 2021 at 12:58pm
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KaphaSound View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 23 July 2020 at 3:03pm
Very new to horn design and genuinely just curious, but what would happen if you cut the top sheet in the same style as the “eye shape” in the Danley BC218s and put 4 together in the same eye configuration? Would you be able to slightly increase the length of the horn this way and gain a bit of extra directivity due to the increased size of the ‘face’ of the stack?

Edited by KaphaSound - 23 July 2020 at 3:04pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2020 at 2:20pm
This is an interesting question, I understand your thinking, I suspect directivity would be improved and you might be right about the slightly increased horn length. This is something I would like to try and measure. I guess I will have to add it to the list of things I would love to do if I wasn't a poor student locked down in an apartment away from my home city.

Would be interested to hear from anyone who has used the BC218.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2020 at 4:17pm
I’d love to help I’m just not 100% confident in hornresp yet, but to get close I assume you’d use 1pi to approximate the large face, then a bit of extra length to get around the final bend at the mouth, but here’s where I get stuck . Would you essentially need to calculate the total horn with 2 or 4 drivers so the combined S1 (S2 for OD) for the compression ratio, then I guess combined S3/4 to keep the expansion rate consistent? Then the total combined mouth size (S5), and then are there any other paramaters like VTC/ATC VRC/LRC that need to double/quadruple according to the number of drivers? I’m really hoping to pick up 4 15s to put under some EV ZLX 15ps as a first project and the B&C BG15 drivers were looking quite appealing. The goal was to make something capable of hitting 30hz, but after some reading I was realizing that’s near impossible in any kind of semi compact/lighterweight format, until I saw your design. So I’d basically love to see if the boundary compliant multiple horns one mouth method could even push f3 a bit lower if only by just a few hz.

Edited by KaphaSound - 26 July 2020 at 8:40pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 02 August 2020 at 10:03am
Sorry for the delayed response, been a little bit busy. 


Originally posted by KaphaSound KaphaSound wrote:

Would you essentially need to calculate the total horn with 2 or 4 drivers so the combined S1 (S2 for OD) for the compression ratio, then I guess combined S3/4 to keep the expansion rate consistent? 


I would keep it simple, I would sim it as 4 seperate horns, this is quite easy, just enter it as one horn, click calculate then click tools > multiple speakers > drag the sliders, for 4 horns I would go 2 parallel, 2 series, this way it will be an 8 ohm, this will give you 1 watt with the default 2.83v for Eg. You dont need to do anything fancy with changing chamber volume sizes to simulate multiple horns. 

The tricky part would be correctly modelling the last part of the horn, I think I know how I would get the correct length for the horn. I would just draw the path in sketchup and measure it. The mouth is a little trickier. 

Modelling the mouth area of this would be simple, it would just be the cross sectional area (LxW). 



But modelling this isn't so straight forward. 


The mouth actually looks smaller and I suspect it is smaller but the reduced mouth area compared to the last picture may be acoustically invisible at the frequencies we are talking about. Similar to hanging a compression driver and horn flare in mouth of a kick bin like an xtro. The horn flare may take up 30% of the cross sectional area at the mouth but does not have a significant effect on the output. 

Feel free to try sim it in hornresp and post it, will be happy to give my 2 cents. Might even get some input from other people. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jo bg Quote  Post ReplyReply Direct Link To This Post Posted: 02 August 2020 at 10:53am
The mouth on the BC subs is actually smaller as you noticed, the horn path restricts at mouth before suddendly increasing with the boundary loading.
So it's not easy to have a regular (expanding) flh act as a Bc sub when stacked, as there would be no such restriction.

The stack will still load better for the bigger mouth and size, but just stacking and a round exit will not make a BC sub.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 15 August 2020 at 9:20am
Sorry for taking a minute to get back here and I don’t mean to turn this into a BC thread because the original design looks great!

I just was also looking at the BG driver and it seems like you really could just add an extra cut to the top sheet, potentially lose a bit of weight and gain a bit of extra F3 on the low end. I actually did end up doing this in hornresp to the best of my knowledge and will post it soon to see what you guys think, but honestly I think the secret sauce to the BC series could be in just the extra surface area and slight extra length from the last bend. If you think about taking a scoop for example notice how you could essentially turn it on its side and gain all that extra width which would bring you closer to 1 pi although of course the mouth would need to be reoriented somehow (and I’m assuming this is why most designs might work best in 4 or more simply because you’re approaching 1 pi space at that point?). Again I’m super new to this but I won’t be surprised if this type of folding becomes more popular. Peep the labda labs DH-18 for example ( https://www.lambda-labs.com/en/products/dh-18 - https://www.lambda-labs.com/en/products/dh-18). They tout the same significant improvements from that particular arrangement but also offer the different stacking options which have different response curves.

Also in terms of necking down at the mouth in the ‘eye’ config, I think I’ve read and definitely noticed in sims that this can help improve sensitivity in the lowest frequencies.


Edited by KaphaSound - 15 August 2020 at 9:27am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 17 August 2020 at 3:03am
Alright so here was the hornresp design. The one thing I noticed is a slight increase in the group delay up to about 33ms but for the improved sensitivity that could still be worth it? Let me know what you think. I basically quadrupled the necessary parameters as I read on the speakerplans site the best way to model a shared mouth horn was to model the entire horn first and then split into 4 sections. I'd really love to hear if there's anything we can do to improve this. I also completely guessed for the extra length/total mouth size so we can dial those in but this is simmed in 2pi so in reality the response might be halfway between 2pi and 1pi.









Also if anyone know of a good way to directly upload images here that would be great. I've read through before but all the suggested websites to grab the image url from are paid only. (Edit: thanks guys)




Edited by KaphaSound - 25 August 2020 at 7:03am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 17 August 2020 at 2:41pm
You can upload images direct to the forum; if replying to an existing thread remember to use the full reply editor accessed by the arrow icon (7th button along in the row of controls immediately above the reply window).
That works best if your images are less than IIRC 1000 pixels wide, it does compress them a bit though even when they're smaller to start with.
If you don't want that compression or want to preserve larger sizes then off-site hosts are where it's at.
I use imgur, which is free and you don't even need to create an account, you can upload directly there and get links to include in your message here.
I've seen others use imgBB and postimage well enough too.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 18 August 2020 at 12:48am
I see you have simmed it as a single horn containing 4 drivers, I strongly recommend you simulate it as 4 horns, one driver each. I think this is a more accurate representation of what you are trying to model. It is also much simpler.  



The best way to upload images here is to use https://imgur.com/upload?beta, Its really simple, you don't even need to make an account. Once you have uploaded it there, wait like 5 seconds then right click the image and click 'copy image address' (assuming you use google chrome). Then just paste that address between {img} {/img} but with square brackets. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2020 at 8:37am
Okay, my curiosity got the better of me and I gave it a go. 


I think these sims are imperfect to say the least, I don't think a boundary extending 700mm out of mouth constitutes 1pi, especially when we are dealing with wavelengths greater than 8 meters in length. I also think its quite hard to capture the geometry of the last segment of the horn with two hornresp segments.

The measurement for horn-length for the last segment may be a bit pessimistic, I made an arc from the middle of the previous segment to the middle of the cutout in the cab (see image 1.). Maybe it should be to the far corner of the cab as this would be the centre of the total mouth if you coupled four cabs together (see image 2.) Let me know what you think. 


Here is what the path looks like - open to suggestions on how to improve it.


4 x regular BG horn in grey, 4 x BG horn with BC mod in black (2pi)

4 x regular BG horn in grey, 4 x BG horn with BC mod in black (1pi)



I suspect this wouldn't be flat to 30hz with an f3 in the high 20s like the sim suggests but I also suspect you would gain some LF response and sensitivity, I think you would have to build 4 cabs and test it to find out for sure. 

Let me know if you have any suggestions to improve the sims. 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doller Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2020 at 10:05am
Great work you two, very interesting stuff. sorry I can't help with the sims bit dumb on that front sorry. 
Correct me if I am wrong but isn't the point of the bc system focused bass. I.e. not so omnidirectional on the dance floor so to speak. So how different would a bass beam sound to bass everywhere if you get what I am trying to say. Can't sim that I guess. This would be an expensive experiment. I am tempted to take a jig saw to my labs and see what happens. maybe a router.
Did the old Celestion boxes with barn doors use the same concept?
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